Mechanical properties of interfaces between dissimilar or similar materials (e.g., grain boundaries) have become the focal point of research in several fields, including composite materials (metal, ceramic and intermetallic matrix composites), tribology, and solid state devices. This is not surprising because the interfaces between dissimilar materials are sites for mechanical stress concentrations and often nucleate the overall failure process.
Interfaces of interest in composite materials exist between fibers and their diffusion barrier coatings or between the fibers and the surrounding matrix material. In the field of tribology, interfaces exist between various types of functional (magnetic, conducting, optical, electrical), protective (thermal barrier, corrosion, wear resistant), or decorative coatings and their underlying substrates. And, finally, metal/ceramic interfaces are of interest in multilayer devices and magnetic disks and head technology. In all the above applications, mechanical properties of the interface (tensile and shear strength, toughness, etc.) often control the overall functionality of the coated part. Therefore, improving the mechanical properties of the interface for a prolonged life of the coated part is of fundamental interest. However, in ceramic and metal matrix composites, where the fiber/coating interface is used to deflect impinging cracks from the matrix, it is often desirable to impair the strength of the interface.